Minimum wear film guide for rolling loop film transport mechanism

ABSTRACT

A film guide mechanism for use in rolling loop film transport mechanisms minimizes film wear and permits higher film speeds on the order of 30 frames per second. The film is sandwiched in its path of travel between a driven inlet drive sprocket and a shock double capstan, the inlet drive sprocket having a plurality of teeth that mate with perforations along each edge of the film and that also mate with grooves in the shock double capstan that is in turn frictionally driven by the driven inlet drive sprocket. The driven inlet drive sprocket and the shock double capstan are slightly concave in shape to prevent contact between these components and the central emulsion area of the film. A fixed inner guide having a radius in an area adjacent the shock double capstan that matches the radius of the shock double capstan and a spring-loaded shock double capstan slide on which the shock double capstan is mounted provide a variable gap to accommodate any backlash or shock rebound of the film as it passes through the gap prior to capture by a rotor of the film transport mechanism. A selectable stop engages the shock double capstan slide to prevent narrowing of the variable gap beyond a predetermined minimum.

REFERENCE TO RELATED PATENT

This application is related to U.S. Pat. No. 4,114,996 entitled InletGuide Structure for Rolling Loop Film Transport Mechanism, the subjectmatter of which is incorporated herein by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates generally to rolling loop film transportmechanisms of the type used to transport photographic film through aprojector, camera or other motion picture apparatus and moreparticularly to a shock absorbing film guide mechanism for prolongingthe life of films employed in such mechanisms.

U.S. Pat. No. 4,114,996 describes a film inlet guide having fixedcomplementary outer and inner guides adapted to receive film from adrive sprocket of a rolling loop film transport mechanism and to guidethe film inwardly toward a path defined between the stator and rotor ofthe film transport mechanism. This prior art film inlet guide isdisadvantageous in several respects. Excessive film wear results fromthe friction created by the film passing the stationary surfaces of theinlet guide, particularly the nose portion of the outer guide. Overtime, this friction produces wear on the nose portion of the outer guideitself, requiring periodic film guide replacement. In addition, a staticcharge is created by the film passing over the stationary nose portionof the outer guide. This static charge attracts dust and other particlesto the film surface immediately prior to projection onto a screen,resulting in magnification of these particles to a size 350 times theiractual size. The nose portion of the outer guide of the prior art filminlet guide causes the film to become rigid as it enters the gap on therotor of the film transport mechanism. When the rigid length of film isimpacted by the rotor segments that are travelling at 180 RPM, the filmis lightly tugged against the teeth of the inlet drive sprocket, therebycausing film wear and/or damage to the perforations along the edges ofthe film. The rigidity imparted to the film by this prior art inlet filmguide becomes an even more significant problem when film speed isincreased from the conventional 24 frames per second to the 30 framesper second at which some projection systems operate. Finally, the filminlet guide of the prior art hinges to an unadjustable indexed positionthat defines a fixed gap between the inlet sprocket and the film guide.Since this gap is fixed, any backlash or shock rebounds of the filmwithin the gap results in additional abrasion of the film surface.

It is therefore the principal object of the present invention to providea film guide mechanism for use in rolling loop film transport mechanismsthat minimizes film wear and therefore prolongs the life of motionpicture film operating at a conventional speed of 24 frames per secondand that facilitates higher speeds on the order of 30 frames per secondthat were previously not attainable using prior art film guidemechanisms.

It is a further object of the present invention to provide a film guidemechanism for use in rolling loop film transport mechanisms thatsignificantly reduces the static charge buildup on the film, resultingin a much cleaner presentation of the film as it is projected onto alarge screen.

It is a further object of the present invention to provide a film guidemechanism for use in rolling loop film transport mechanisms thatprevents rigidity of the film as it exits the film guide mechanism,thereby reducing the force with which the film impacts the rotor and, asa result, minimizing wear on the film and the film guide mechanismitself.

It is a further object of the present invention to provide a film guidemechanism for use in rolling loop film transport mechanisms that permitseasy adjustment, within a particular range, of a film exit gap between ashock double capstan and a fixed inner film guide.

It is a further object of the present invention to provide a film guidemechanism for use in rolling loop film transport mechanisms thatincludes a shock absorber that permits variability of the film exit gapduring operation in response to backlash and rebounding of the film asit passes through the film exit gap, thereby eliminating stress on thefilm perforations imparted by the teeth of the driven inlet drivesprocket.

These and other objects are accomplished in accordance with theillustrated preferred embodiment of the present invention by providing adriven inlet drive sprocket having a plurality of teeth that mate withperforations along each edge of the film and that also mate with groovesin a shock double capstan that is in turn driven by the driven inletdrive sprocket, thereby sandwiching the film therebetween. The driveninlet drive sprocket and the shock double capstan are slightly concavein shape so that no contact is made between these components and theemulsion area of the film. A fixed inner guide has a radius in an areaadjacent. The shock double capstan that matches the radius of the shockdouble capstan itself to provide a variable gap to accommodate anybacklash or shock rebound of the film as it passes through the gap. Thegap is made variable by a shock absorber assembly coupling the shockdouble capstan to an adjusting screw via a spring. The spring constantof the spring is set by means of the adjusting screw, thereby allowingthe gap to vary in response to any shock rebounds of the film that mayoccur within the gap.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the film guide mechanism of the presentinvention.

FIG. 2 is a sectional view of a portion of the film guide mechanism ofFIG. 1 illustrating the relationship between the film, an driven inletsprocket, and an inlet guide housing.

FIG. 3 is a sectional view of a portion of the film guide mechanism ofFIG. 1 illustrating a double capstan shock absorber assembly.

FIG. 4 is a sectional view of a portion of the film guide mechanism ofFIG. 1 illustrating the relationship between a shock double capstan andguide spool fingers that act to prevent the film from wrapping aroundthe shock double capstan.

FIG. 5 is a sectional view of a portion of the film guide mechanism ofFIG. 1 illustrating the position of the film with respect to the driveninlet drive sprocket and the film guide.

FIG. 6 is a sectional view of a portion of the film guide mechanism ofFIG. 1 illustrating the details of a stop that establishes a minimum gapbetween a shock double capstan and an inner guide.

FIG. 7 is a sectional view of a portion of the mechanism of FIG. 6illustrating the details of operation of the stop.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is shown a driven inlet drive sprocket 12that drives film 13 through an inlet guide housing 9, following a pathbetween driven inlet drive sprocket 12 and a shock double capstan 15,between shock double capstan 15 and an inner guide 17, and over a pairof top and bottom guide spool fingers 16, after which it is contacted byrotor segment 11. The inlet guide housing 9 comprises an outer guide 14,shock double capstan 15, and the pair of guide spool fingers 16. Driveninlet drive sprocket 12 and shock double capstan 15 are shaped to haveslightly concave outer surfaces so that only the perforated top andbottom edges of the film 13 contact those components, therebyeliminating the opportunity for damage to the central emulsion area ofthe film 13 that contains the images to be projected. The shock doublecapstan 15 is frictionally driven by a friction O-ring 22, illustratedin FIGS. 3, 5, and 7, that is attached to the top of shock doublecapstan 15 and is in engagement with driven inlet drive sprocket 12.During operation of the rolling loop film mechanism in which the filmguide of the present invention is employed to guide film 13, shockdouble capstan 15 is pressed against driven inlet drive sprocket 12,thereby causing shock double capstan 15 to rotate in the oppositedirection. Since shock double capstan 15 rotates at the same speed asthe film 13, abrasion of film 13 and static charge buildup thereon areminimized. The pair of guide spool fingers 16, attached to the outerguide 14 using flat head screws, for example, serve to prevent the film13 from wrapping itself around the shock double capstan 15 as it exitsthe film guide. Inner guide 17 has a radius in an area adjacent shockdouble capstan 15 that matches the radius of shock double capstan 15 toprovide a variable gap 30 to accommodate any shock rebound of film 13 asit passes through the variable gap 30. Shock double capstan 15 includestop and bottom grooves 32, 34, as illustrated in the sectional diagramof FIG. 4, that mate with the teeth on driven inlet drive sprocket 12 inorder to capture film 13 therebetween.

Referring now to the sectional diagram of FIG. 2, it may be seen thatfilm 13 passes between the outer guide 14 and driven inlet drivesprocket 12. Top and bottom grooves 36, 38 in outer guide 14 accommodatethe teeth on the periphery of driven inlet drive sprocket 12. A cap 27atop driven inlet sprocket 12 includes a drive surface that engagesfriction O-ring 22 mounted on shock double capstan 15 for the purpose ofdriving shock double capstan 15.

Referring now to the sectional diagram of FIG. 3, it may be seen that asfilm 13 is impacted by rotor segment 11 of FIG. 1 as it exits the filmguide, the double capstan slide 24 loads against a spring 25, the springconstant of which is set by means of an adjusting screw 26. The settingchosen for adjusting screw 26 is determinative of the force that must beovercome by film 13 as it travels through the film guide in order towiden variable gap 30 in response to any backlash or shock rebound offilm 13. An O-ring retainer 23 is positioned on top of shock doublecapstan 15 to retain friction O-ring 22 in position for engagement bydriven inlet drive sprocket 12, as illustrated in more detail in FIG. 5.

Referring now to the sectional diagram of FIG. 4, it may be seen thatthe pair of top and bottom guide spool fingers 16, attached to outerguide 14, prevent the film 13 from wrapping around shock double capstan15 when exiting the film guide mechanism.

Referring again to the sectional diagram of FIG. 5, it may be seen howfilm 13 is sandwiched between driven inlet drive sprocket 12 and shockdouble capstan 15. As stated above in connection with the description ofFIGS. 1 and 3, shock double capstan 15 is driven by a frictional O-ring22 that is attached thereto in position for driving engagement withdriven inlet drive sprocket 12.

Referring now to the sectional diagrams of FIGS. 6 and 7, it may be seenhow a selected one of two stops 20 and 40 mounted in outer guide 14 maybe positioned to engage shock double capstan slide 24 to limit theforward travel of shock double capstan slide 24 and of shock doublecapstan 15 itself. This limitation establishes a minimum width forvariable gap 30 between shock double capstan 15 and inner guide 17 tothereby prevent pinching and resultant excessive wear of film 13 as ittravels within variable gap 30. Since the desired minimum width forvariable gap 30 is a function of film speed, an appropriate one of thetwo stops 20 and 40 may be rotated into position in engagement withshock double capstan slide 24 by means of a film speed indicator knob 21located on the front face of outer guide 14.

I claim:
 1. A film guide mechanism for receiving photographic film to beprojected by a rolling loop film transport mechanism and for guiding thephotographic film into position for engagement by a rotor of saidrolling loop film transport mechanism, the film guide mechanismcomprising:a circular inlet drive sprocket having a plurality of teethspaced around a peripheral surface thereof at top and bottom edgesthereof for engaging top and bottom perforations in the film, said inletdrive sprocket adapted for driven rotation so as to pull the film from afilm supply; circular shock double capstan means positioned tangentiallyadjacent to said inlet drive sprocket and adapted to be rotationallydriven by said inlet drive sprocket in a direction opposite said inletdrive sprocket, said shock double capstan means having top and bottomgrooves in a peripheral surface thereof for receiving the plurality ofteeth of said inlet drive sprocket, the film passing between said inletdrive sprocket and said shock double capstan means; outer guide meanshaving a concave curved surface adjacent to and complementary with saidinlet drive sprocket for maintaining the film in engagement with saidplurality of teeth of said inlet drive sprocket; inner guide meanspositioned on a side of said inlet drive sprocket and said shock doublecapstan means opposite from said outer guide means, said inner guidemeans having a concave curved surface adjacent to and complementary withsaid shock double capstan means, a film exit gap through which the filmpasses being defined between the peripheral surface of said shock doublecapstan means and the concave curved surface of said inner guide means.2. A film guide mechanism as in claim 1 further comprising spring-loadedslide means coupled to said shock double capstan means for permittingtranslational motion of said shock double capstan means with respect tosaid concave curved surface of said inner guide means to thereby permitsaid film exit gap to vary in response to backlash and shock reboundingof the film as it passes through said film exit gap.
 3. A film guidemechanism as in claim 1 wherein the peripheral surface of each of theinlet drive sprocket and shock double capstan means is concave toprevent contact with a central emulsion area of said film.
 4. A filmguide mechanism as in claim 1 wherein said shock double capstan meansfurther comprises retainer means and an O-ring retained within saidretainer means, said shock double capstan means being rotationallydriven by frictional coupling between said 0-ring and said inlet drivesprocket.
 5. A film guide mechanism as in claim 1 wherein saidspring-loaded slide means includes stop means for selecting a minimumwidth of said film exit gap.
 6. A film guide mechanism as in claim 1wherein said outer guide means includes finger means adjacent said shockdouble capstan means for guiding the film out of the film guidemechanism and preventing the film from wrapping around said shock doublecapstan means.